Explosive forming with inertia means



Oct. 30, 1962 E. A. STABA 3,060,379

EXPLOSIVE FORMING WITH INERTIA MEANS Filed Feb. 4, 1959 TO VACUUM PUMPTO VACUUM PUMP INVENTOR.

EDWARD A. STABA States ginia Filed Feb. 4, 1959, Ser. No. 791,182 1Claim. (Cl. 113-51) ite The present invention relates to metal workingand in particular relates to methods for fusing or welding as well as toforming to given shapes.

More particularly, the invention relates to schemes for working orwelding metal where the work piece is generally in the form of a sheetor in a form wherein the ratio of surface area to thickness is high. Thebasic steps involved usually embrace disposing one or more Work piecesparallel to one another or to a half die having a desired contour,placing an explosive in the form of a coating or in the form of aparticular pattern upon or immediately adjacent one of the sheets andthereafter detonating or activating the explosive with the result thatone sheet is driven toward the other or toward the forming die, as thecase may be.

A particular feature of the invention is the provision of a process forfabricating a panelled structure having in ternal conduits.

Another feature of the invention is the provision of a process forforming or working metal utilizing exposives where the kinetic energydeveloped by the explosive is controlled or moderated in a novelfashion.

A further feature of the invention is the provision of a process forfabricating conduit structure, such as those used in heat exchangers orevaporators, utilizing explosives.

An additional feature of the invention is the provision of a process forfabricating a sheet metal blank in accordance with a predeterminedcontour, pre-formed in a die, where the die structure utilized is a onepart die.

Before discussing the details of the particular embodiments of theinvention, it is well to point out that the prior art is replete withschemes for welding or forming metal utilizing explosives. However, thepresent invention utilizes a new phenomenon observed in the course ofexperimental work in connection with the development of apparatus andprocesses for welding and forming explosively.

It is well known that when two sheet metal blanks have been disposed sothat one sheet is firmly supported on a rigid base while the secondsheet is arranged generally parallel but spaced apart by suitablespacers, such as by lengths of drill rod or the like, the application ofan explosive force to the upper sheet drives the sheet towards the lowersheet with explosive violence.

It has been observed that fusion of the two sheets occurs only in theareas where the upper sheet has been unsupported. For example, the areasof the sheet that are separated by an air gap fuse with one anotherwhile the areas of the sheet that bear upon the drill rod are not fusedor welded.

It has been theorized that this local or regional fusion occurs becausein the unsupported areas, sutficien-t kinetic energy is developed byvirtue of the spaced condition of the sheets to permit an exceedinglyhigh velocity to develop in these areas of the sheet so that upon impactthe kinetic energy acquired or developed by the moving region of theblanks is immediately converted into heat energy with resulting surfacefusion.

In contrast, the regions of the blank which are disposed in contact withthe spacer cannot develop kinetic energy because motion is prevented bythe spacer, thus there is no sudden conversion of kinetic energy intoheat.

Thus, it has been observed that where welding is de- 3,660,879 PatentedOct. 30, 1962 sired, it is merely necessary to provide an air gapbetween the two sheets; correspondingly, in those regions where nowelding is desired, it is necessary to inject a spacer in the form of arigid or semi-rigid member having the desired shape of contour. Uponactivation of the explosive those regions of a pair of plates whichstraddle an air gap are welded or fused while those regions whichstraddle a spacer member are not fused to one another nor are they fusedto the spacer.

Another phenomenon has been observed particularly in connection withforming a single sheet against a half die where the half die is formedwith a contour to be transferred or impressed upon the blank. In asituation where the contoured die contains ribbed or raised portions andintermediate valleys or grooves, there has been a tendency for weldingto occur when welding is not desired. That is, in those areas of the diewherein an air gap exists between the die face and the surface of theblank or work piece, fusion sometimes occurs while in the regions of thedie in which there are projections which bear upon or come just short ofbearing upon the blank, welding does not occur.

Accordingly, the present invention deals with a method for eliminatingwelding where only a forming operation is desired even though there issubstantial gap between the blank and valleys or grooves in thecontoured die.

A process embracing certain principles of the present invention mayinclude the steps of disposing a pair of panels in generally parallelarrangement, spacing the panels apart by interposing therebetween atleast one 1 spacer element so that certain parts of both panels bearupon the spacer while other regions thereof straddle an air gap, placingan explosive over one panel, activating the explosive effective tocreate a force which drives the panels into fused or welded contact onlyin the regions thereof straddling an air gap.

Another embodiment of the invention may include the steps of providing ahalf die formed with a desired contour, said contour including raisedportions and recessed portions to define lands and grooves or the like,disposing a deformable blank of sheet material over the die, disposingan inertia member above the blank, placing an explosive material incontact with or immediately adjacent the inertia member and activatingthe explosive material with the result that the blank and the inertiamember are driven towards the forming die, said inertia member beingeffective to attenuate or moderate motion of the blank towards the dieto preclude fusion or welding between the blank and the die.

Other features and advantages of the present invention will becomeapparent from the succeeding specification when read in conjunction Withthe appended drawings in which:

FIG. 1 shows a typical fixture which may be utilized in practicing oneembodiment of the present invention;

FIG. 2 is a sectional view of a panel structure containing conduitsformed in the fixture of FIG. 1;

FIG. 3 shows an additional fixture utilized in practicing anotherembodiment of the present invention; while,

FIG. 4 is a sectional view of a formed blank shaped in accordance-withthe contour of the half die of FIG. 3.

Referring now in detail to the drawings, there is shown in FIG. 1 a baseplate 10 having a generally flat surface 11 on which there is disposedthe lower panel of a pair of panels 12 and 13. Note that the panel 12lies flat on the surface 11 and the panel 13 is spaced therefromvertically by the spacer elements 14 and 16. The spacer elements cantake a variety of shapes and forms and may be fabricated from rigid,semi-rigid material, metallic or plastic, including low meltingcompositions. In the disclosed embodiment, the spacers 14 and 16comprise lengths of half round metallic bar stock.

The upper panel 13 is coated with an appropriate explosive 17 and isfixed with a detonator 18. The complete assembly including the panels,explosive coating and a detonating fuse 19 are enclosed in a flexiblediaphragm 21 which engages the base block around the periphery thereof,as at 22, and is rigidly attached thereto by an appropriate adhesivesealing compound indicated by the reference numeral 23. It has beenfound that a rubber or plastic sheet material provides a satisfactorydiaphragm especially where the forming is accomplished under fluids suchas water.

The base block 10 is provided with a conduit 24 communicating with theinterior of the diaphragm and with a vacuum pump (not shown) so that thearea under the diaphragm may be evacuated if desired.

The explosive fusion and forming is accomplished in the fixture of FIG.1 wherein upon activating the detonator 18, the fuse 19 is operative toactivate the explosive coating 17. Immediately the regions of the panel13 which are unsupported begin to accelerate and are driven towards thecorresponding regions of the plate 12 so that upon impact therewith,kinetic energy developed, quickly converts into heat energy and fusionoccurs between these regions of the panels 12 and 13.

In contrast, the regions of the panel 12 which bear upon or are close tothe spacers 14 and 16 do not develop as much kinetic energy andconsequently do not develop enough heat energy to fuse to the spacers.

' After the explosive coating has been activated, the spacer members 14and 16 are removed .and paneled structure having a cross sectionalconfiguration as shown in FIG. 2 is fabricated. The areas labelled 26represent occurrences of fusion between the panels 12 and 13 while theintervening conduits 27 result after removal of the spacer members.

Referring now to FIG. 3, there is shown .a base block 30 having a flatsurface 31 on which there is disposed a half die indicated generally bythe reference numeral 32.

The half die is formed with a ribbed or irregular contour comprising aplurality of raised portions such as at 33 and 34 with interveningdepressions or grooves 36 and 37. Disposed over the die is a blank ofdeformable sheet material such as sheet material 38. Disposed above theblank 38 is an inertia member or inertia block 39.

Although the inertia member in the disclosed embodiment of the inventioncomprises a sheet of lead, it is anticipated that a wide variety ofmaterials may be utilized depending upon the particular sheet materialbeing formed, the explosive utilized and the conformation of the halfdie block.

The inertia block is coated with explosive material 41 and is fixed withan appropriate fuse 42 in turn connected with a detonator 43.

The process may be conducted under a head of fluid if desired.

As in the arrangement of FIG. 1, the complete assembly embracing thehalf die, the blank to be formed and the inertia member, is enclosedwithin a diaphragm 44 in the same general way as described with respectto FIG. 1.

Upon activating the explosive, the force generated tends to drive theblank 38 towards the half die so that the blank takes the configurationof the die to produce the cross section shown in FIG. 4.

Ordinarily those portions or regions of the blank 38 which are spacedfrom th surface of the forming die by an air gap will fuse or tend tofuse to the die while those regions of the blank which bear upon or aredisposed very close to the die will merely be formed and remain free ofthe die.

However, by virtue of the introduction of the inertia member theexplosive force is moderated and the mass of the block reduces thevelocity with which the blank approaches the die so that sufiicientkinetic energy is never developed to bring about fusion upon impact ofthe blank with the die.

The energy absorbed by the inertia block is applied to the work piece ina more sustained way as against a sudden shock so that a satisfactoryreproduction of the die is achieved without rupture of the blank orwithout fusing the blank to the die.

Obviously an inertia block may be fabricated of a wide variety ofmaterials and as stated previously must be selected in accordance withthe characteristics of the metal being formed, the intricacy of the diepattern and the explosive utilized.

7 Here again, the process may be conducted under a head of fluid and maybe evacuated, if desired.

It is anticipated that a Wide variety of modifications and changes maybe devised in the several embodiments of the disclosed invention withoutdeparting from the spirit and scope thereof.

What is claimed is:

The method of forming a sheet metal article to a predetermined contourcomprising the steps of (a) providing a die having a forming surfacecorresponding to said contour,

(b) placing a deformable blank of sheet metal having two opposite sideswith one of said sides facing said surface,

A (c) placing an explosive over an area of said blank on its other side,said blank and explosive being such that said explosive when set offwould normally drive said blank against said surface to effect not onlydeformation of said blank, but also at least one of fracture of saidblank, fusion of said blank, and welding between said blank and die,

(d) interposing an inertia member between said blank and explosive insaid area, said inertia member 7 carrying said explosive as a coating,

(e) setting off said explosive to drive said blank into contact withsaid forming surface at a velocity moderated by said member to effectdeformation of said blank to said contour, said member having propertiesbeing adapted to moderate said velocity to prevent said fracture,fusion, and welding.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Steel Publication, Aug. 25, 1958, p. 84,

